Typically, as shown in FIG. 1, a wireless communication system comprises elements such as client terminals or mobile stations and one or more base stations. Other network devices may also be employed, such as a mobile switching center (not shown). As illustrated in FIG. 1, the communication path from the base station (“BS”) to the client terminal or mobile station (“MS”) is referred to herein as a downlink (“DL”) direction or downlink channel, and the communication path from the client terminal to the base station is referred to herein as an uplink (“UL”) direction or uplink channel. In some wireless communication systems, the MS communicates with the BS in both the DL and UL directions. For instance, such communication is carried out in cellular telephone systems. In other wireless communication systems, the client terminal communicates with the base stations in only one direction, usually the DL. Such DL communication may occur in applications such as paging. As used herein, the terms “base station” and “network” are used interchangeably.
Normally, the transmission intervals in downlink channel or in an uplink channel spans certain predefined duration and it is referred to as “frame” herein. A frame duration may be different for different communication systems and normally it is on the order of a few milliseconds. For example, the frame duration may be 5 milliseconds. Typically in a wireless communication system, the client terminal and the base station may transmit information in blocks of data and such a block of data is referred herein as a “message.”
Normally, certain types of system information may be required by all client terminals so that they may communicate with the wireless communication network. The system information typically includes synchronization information, system parameters, allocation information, paging information, etc. The wireless communication network may transmit such system information as broadcast data so that all client terminals within its coverage area may be able to receive and such information is herein referred to as “broadcast messages.” Typically in a wireless communication system sometimes a base station may transmit some information that may be addressed only to a group of client terminals and such messages are herein referred to as “multicast messages.” Examples of multicast messages include multimedia information about sports, news, traffic, weather, etc. Typically in a wireless communication system the base station may transmit messages that are uniquely addressed to a particular client terminal and such messages are herein referred as “unicast messages.” An example of a unicast message is user specific payload data.
Typically, in wireless communication systems many client terminals are handheld portable battery operated devices. Hence it is important for the client terminals to operate in a power efficient manner. To reduce power consumption, the client terminal may turn off most of its hardware and software components when it is not required to receive in downlink direction or transmit in uplink direction. From a Power Management (PM) perspective, the state of the client terminal in which it may turn off most of its hardware and software components is referred herein as “PM sleep state.” The state in which the client terminal is involved in downlink data transfer or uplink data transfer or in transfer in both directions is referred herein as “PM active state.”
The transition from PM sleep state to PM active state of the client terminal is referred herein as “wake-up” state. The transition from PM active state to PM sleep state of the client terminal is referred to herein as “entering-sleep” state.
The wake-up state and the entering-sleep state may have overhead in power consumption. Normally the power consumption may be higher during both the wake-up state and the entering-sleep state when compared to that of the PM sleep state. Also normally the power consumption may be lower during both the wake-up state and the entering-sleep state when compared to that of the PM active state. Typically the transition time for the wake-up state is longer than the transition time for the entering-sleep state. Also in general the power consumption during the wake-up state may be higher than that of during the entering-sleep state. An example of PM sleep state to wake-up state then to PM active state then to entering-sleep state and then back to sleep state transitions in a battery operated client terminal is illustrated in FIG. 2. As and when appropriate, the client terminal may enter into PM sleep state and PM active state and an example is illustrated in FIG. 3. For the description of the present disclosure herein, the wake-up state and the entering-sleep state may not be explicitly discussed or shown in the drawings but they always exist.
The client terminal may transition from PM sleep state to PM active state to receive in the downlink or transmit in the uplink or both. Some hardware and software components may be specific to receive in the downlink or transmit in the uplink and they may be independently turned on or turned off based on receive in the downlink or transmit in the uplink respectively. Some hardware and software components in the client terminal may be common for both receive in the downlink and transmit in the uplink and may have to be turned on for either receive in the downlink or transmit in the uplink.
Typically, a client terminal may operate in one of five different functional states: (i) power-on state; (ii) idle state; (iii) access state; (iv) connected state and (v) power-save state. Typical functional state transitions in a client terminal are illustrated in FIG. 4. Typically, in the power-on functional state the client terminal may check for the available base stations, may synchronize with the network and may attempt to camp on to the best suitable base station. Typically, in the idle functional state the client terminal may check and/or periodically receive broadcast and/or multicast messages in the DL direction. Typically, in the access functional state, the client terminal may access the base station to establish connection with the base station. Typically, in the connected functional state the client terminal and the base station may communicate with each other through DL and/or UL to receive and/or to send control information and/or user payload data, may receive broadcast messages and/or may receive multicast messages. In the connected functional state the client terminal may operate in PM active states in all the frames and may operate in PM sleep states within the frame. Typically, in the power-save functional state the client terminal and the base station may communicate with each other through DL and UL to send and receive control information and/or user payload data, may receive broadcast messages and/or may receive multicast message. In power-save functional state the client terminal may operate in PM active states in frames when there is data to receive in DL and/or when there is data to send in UL and in other frames it may operate in PM sleep state.
Once a client terminal is turned on, it may camp onto the wireless communication network, may receive the latest network information, may register to the network, may periodically receive the latest network information, and may be ready to establish connection with the wireless communication network. For a battery operated client terminal, to increase the battery usage time, it is desirable to operate a client terminal in the PM sleep state as much as possible without compromising user experience.
A base station to which the client terminal may be downlink synchronized and/or communicating with at any given time is referred herein as the Serving Base Station (SBS). In some wireless communication systems the serving base station is normally referred to as the serving cell. The base stations that are in the vicinity of the serving base station are called Neighbor Base Stations (NBS). Similarly, in some wireless communication systems a neighbor base station is normally referred to as a neighbor cell. While in practice a cell may include one or more base stations, distinction is not made between a base station and a cell, and such terms may be used interchangeably herein.
After initially synchronizing with a cell, a client terminal may switch to another cell depending on the signal conditions, network congestion, and other criteria. The process of switching from one cell to another cell by a client terminal is often referred as handover (“HO”) or cell reselection. In some wireless communication systems handover is also referred to as handoff. Also in some wireless communication systems cell reselection is also referred to as idle mode handoff. Normally, in mobile wireless communication systems, client terminals switch over from one cell to another as signal conditions change. The signal conditions may change due to the movement of the client terminals or due to change in network traffic conditions or change in the surroundings of the client terminal or the combination of any of these factors. An NBS to which a client terminal may be switching over its communication from the current SBS is herein referred to as Target Base Station (TBS). In some wireless communication systems a target base station is normally referred to as a target cell. Sometimes during a handover, the serving cell and the target cell may be the same and only the channel used for communication may be changed. Such a handover, in which the cell is not changed, is called an intra-cell handover. The purpose of intra-cell handover may be that the new channel is better suited for communication than the previous channel within the same cell.
The decision making process for handovers and cell reselections varies from one wireless communication system to another. However, the decisions are generally based on the signal conditions measurements by the client terminals and reporting of those measurements to the wireless communication network by the client terminals. The wireless communication network generally may influence and control the measurements and reporting process of the client terminal by providing parameters for the measurement and reporting process. The actual decision to perform handover may be made either by the network or by the client terminal depending on the type of particular wireless communication system. On the other hand the cell reselection decisions in idle mode may be generally performed autonomously by the client terminal. Both Handovers and cell reselections may normally lead to change of cell from which the client terminal may access communication services. The difference between the handover procedure and cell reselection procedure depends generally on whether a client terminal is engaged in an active connection with the wireless communication network. The term handover may be used herein to refer to handover or cell reselection or both. The actual process of handover or cell reselection may be inferred based on the context.
Typically in a wireless communication the base station may group the system information and each group of system information may be transmitted as multiple broadcast messages and such broadcast messages are herein referred as system parameter messages. The system parameter messages may carry important system information without which the client terminal may not be able to communicate with the wireless communication network. The wireless communication network may transmit these system parameter messages at regular intervals in such a way that any client terminal that enters its coverage area may receive these system parameter messages and may be able to communicate with the wireless communication network at the earliest possible time. Client terminals that are already in the base station's coverage area may also periodically receive these system parameter messages for possible updates. Normally a client terminal may store the system parameter messages in its memory for the current SBS.
Typically, system parameter messages may carry a Configuration Change Count Indicator (CCCI) parameter. Normally a base station may change the value of CCCI in the system parameter message to indicate to the client terminals about the change in the information in that system parameter message. A client terminal may check the value of the CCCI to identify if any of the information in a system parameter message has been changed. If the value of CCCI has not changed, a client terminal may not receive and/or may not process the remaining part of that system parameter message. If the value of CCCI has changed, then the client terminal may receive and may process that system parameter message to get the updated information in that system parameter message.
Typically, in some wireless communication systems where there may be multiple system parameter messages broadcast by a base station, all system parameter messages may carry the same value of CCCI. In some wireless communication systems where there are multiple system parameter messages broadcast by a base station, one or more system parameter messages may carry a different value of CCCI. In some wireless communication systems where there are multiple system parameter messages broadcast by a base station, each system parameter message may carry different value of CCCI.
Typically, in some wireless communication systems, the base station may periodically transmit broadcast messages which may have the CCCI(s) of system parameter messages. The broadcast message that carries the CCCI(s) of system parameter messages is herein referred to as page message. Typically when there is a change in one or more of the system parameter messages, the base station may change the value of CCCI(s) in those system parameter messages and may change the value of the corresponding CCCI(s) in the page message. When a client terminal receives a page message, it may check the values of CCCI(s) for any change in the system parameter messages. If the value(s) of CCCI(s) are not changed, the client terminal may not receive or may not process those system parameter messages. If the value(s) of CCCI(s) are changed in the page message, then the client terminal may receive and may process those system parameter messages to get the updated information in those system parameter messages.
In some wireless communication systems, the client terminals may be required to periodically receive certain system parameter messages for the selective list of NBSs in addition to receiving the system parameter messages of the SBS. For such wireless communication systems, the client terminals may be required to periodically update the system parameter messages if there is any change in them for the selective list of NBSs in the similar manner the client terminal updates the system parameter messages for the SBS. The period at which the client terminal may have to update the system parameter messages for the SBS and for the NBS may be different. For example, in Global System for Mobile Communications (GSM), the client terminal may be required to receive system parameter messages for the SBS and/or certain system parameter messages for the selective list of NBSs and the period to update the system parameter messages may be different for the SBS and the NBSs. Typically, for a given SBS, the selective list of NBSs is normally broadcast by the SBS.
Typically, in wireless communication systems, most of the system parameter messages may not change frequently. For example, some system parameter messages may change once or twice a day and some system parameter messages may not change for many days.
Typically, when a client terminal switches to a new base station due to cell reselection or handover, it may be required to receive system parameter messages for the new SBS. In some wireless communication systems, when a client terminal switches to a new base station due to cell reselection or handover, it may be required to receive the system parameter messages for the new SBS and certain system parameter messages for the selective list of NBSs corresponding to the new SBS.
In wireless communication systems, the normal use case scenario of a client terminal may be to operate in a specific geographical area. For example, one typical use case scenario of a portable battery operated client terminal, such as a cellular handset during weekdays of a week, may be that a user may carry the mobile client terminal from home to work and nearby areas and back to home. For this typical use case scenario, a client terminal may get service from a set of base stations in the wireless communication network. FIG. 5A illustrates an example use case scenario, in which a user may carry the client terminal from home (“A”) to work (“B”) and back from work (“B”) to home (“A”) during weekdays of a week. For this example use case scenario, a client terminal may get service from base stations 2, 4, 3, 6 and 9 while the user carries the client terminal to go from home to work and the client terminal may get service from base stations 9, 6, 3, 4 and 2 when the user carries the client terminal to go from work to home. Another typical use case scenario may be that the user for most of the time may use the client terminal at home (“C”) as shown in FIG. 5B and the client terminal may get service from base stations 4, 6 and 7 and may do frequent handover or cell reselection based on the available service quality from the base stations 4, 6 and 7. Yet another typical use case scenario is that a user may use a client terminal at work (“D”) as shown in FIG. 5B during the work hours and the client terminal may get service from base stations 10, 12 and 13 and may do frequent handover or cell reselection based on the available service quality from the base stations 10, 12 and 13.
Normally the client terminal may operate in the functional idle state for most of the time. In the idle state the client terminal may be required to periodically receive and update the system parameter messages and may be required to receive the multicast messages. As the signal conditions change, a client terminal may perform cell reselection or handover to get the service from a more suitable cell. When the client terminal switches to a different cell, it may be required to receive all the system parameter messages for the new SBS as well as may be required to receive certain system parameter messages for the selective list of cells that are NBSs for the new SBS. In traditional client terminals, once a client terminal switches to a new cell it may not keep the system parameter messages of the previous SBS. Also in some wireless communication systems where a client terminal may be required to periodically receive system parameter messages of the selective list of NBSs, when a client terminal switches the SBS, the selective list of NBSs for the current SBS also may change and a traditional client terminal may discard the system parameter messages of the base stations that are not part of the current serving base station's NBSs list.
The set of all system parameter messages broadcast by a base station is herein referred to as “base station broadcast system information.” Similarly the set of all multicast information transmitted by a base station is herein referred to as “base station multicast system information.”